How to create a zero size view of a Buffer with bind groups

[Pauan]

I am creating a utility that copies a Vec<T> into a Buffer, so that way I can easily send data to the GPU.

When the Vec<T> increases in size, I want to automatically resize the Buffer.

The way that I'm doing this is simple: I create a Buffer that is the same size as vec.capacity():

let size = vec.capacity() * std::mem::size_of::<T>();

let buffer = device.create_buffer(&BufferDescriptor {
    label: ...
    size: size,
    usage: ...
    mapped_at_creation: true,
});

And whenever the Vec capacity changes, I destroy the old Buffer and create a new Buffer with the new capacity.

I use the capacity instead of the len because I don't want to constantly recreate the Buffer, I want to amortize the cost of recreating the Buffer.

But the capacity of the Vec is larger than the len of the Vec, so I need to create a slice of the Buffer which only contains the len of the Vec.

I can do that easily with buffer.slice:

// Calculate byte size of the Vec
let size = vec.len() * std::mem::size_of::<T>();

buffer.slice(..size)

However that only works for vertex buffers and index buffers. When I try to create a bind group, I run into an issue:

// Calculate byte size of the Vec
let size = vec.len() * std::mem::size_of<T>;

let bind_group = device.create_bind_group(&BindGroupDescriptor {
    label: None,
    layout: ...
    entries: &[
        BindGroupEntry {
            binding: 0,
            resource: BindingResource::Buffer(BufferBinding {
                buffer: &buffer,
                offset: 0,
                size: NonZeroU64::new(size),
            }),
        },
    ],
});

In this case, if vec.len() is 0 then this fails, because the size of a BufferBinding cannot be 0.

[cwfitzgerald]

The simple answer is that you can't - you need to keep the buffer no smaller than the minimum binding size of the binding (which in the case of an array, is the size of a single element)

[Pauan]

So you're saying that it's completely impossible to have a uniform buffer which is empty?

[cwfitzgerald]

You can have a buffer which is empty, you just can't construct a shader which it is valid to bind to.

[Pauan]

Alright, I'll have to figure out a different solution then, thanks for your help!